A solution of liquid soap and water, or a bottle of children's soap bubble solution are the best options. The soap bubble solution is a little better since it will stay on the joint longer and thus detect a smaller leak.

: What is the best way to check for a propane leak inside the house? It may sound silly, but I have considered smelling each joint, but is there a tool or some more professional way? When I find the leak, must I take it apart and redo to seal the leak, or is there something to put around the joint that will seal it? Thanks!